Hybrid multifunctional posterior interspinous fusion device

ABSTRACT

An interspinous stabilization device is provided that more evenly distributes loads throughout the adjacent vertebrae than known interspinous stabilization devices, and further can readily compensate for graft settling so as to maintain continued axial loading of the graft material.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. Ser. No. 14/379,139filed Aug. 15, 2014, now U.S. Pat. No. 10,188,434 issued Jan. 29, 2019,which is a national stage application filed under 35 USC § 371 ofinternational application PCT/US2013/026665 filed Feb. 19, 2013, whichclaims the priority to United States provisional application Ser. No.61/599,988 filed Feb. 17, 2012, the disclosure of which is incorporatedherein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

BACKGROUND OF THE INVENTION

This invention relates in general to an improved structure for a hybridmultifunctional posterior interspinous fusion device.

An interspinous stabilization device is a device that is adapted to besecured to two or more adjacent vertebrae of a spine in order tostabilize the relative positioning therebetween. An interspinousstabilization device can also be used to facilitate the placement of abone-growth material, such as a bone graft material, between suchadjacent vertebrae to enhance bone growth and promote fusion of theadjacent vertebrae.

Wolff s law of dynamic osteosynthesis states that every change in thefunction of a bone is followed by definitive changes in its internalarchitecture and secondary alterations in its external confirmation.This means that osseous tissues remodel in direct response to thestresses placed upon them. Although known interspinous stabilizationdevices have functioned satisfactorily for stabilizing the relativepositioning of the adjacent vertebrae to which they are connected, theyare not well suited for desirably maintaining axial compression on abone graft material that is disposed between such adjacent vertebraeafter graft settling occurs, such as described in Wolff s law. Thus, itwould be desirable to provide an improved structure for an interspinousstabilization device that more evenly distributes loads throughout theadjacent vertebrae than known structures, and further readilycompensates for graft settling so as to maintain continued axial loadingof the graft.

SUMMARY OF THE INVENTION

This invention relates to an improved structure for an interspinousstabilization device that more evenly distributes loads throughout theadjacent vertebrae than known interspinous stabilization devices, andfurther readily compensates for graft settling so as to maintaincontinued axial loading of the graft.

More specifically, this invention relates to a medical device that helpsin performing a spinal fusion procedure by holding the bone graft inplace and stabilizing the facet screw by a plate that is attached to it.The invention also performs a dynamic function that compensates forsettling of the bone graft over time. This dynamic function may, ifdesired, be enhanced by a movement-limiting mechanism that allowsextension but not flexion such that the bone graft fusion remains incontact and fusion takes place. Thus, the interspinous stabilizationdevice of this invention is a multipurpose device that both more evenlydistributes loads throughout the adjacent vertebrae than knowninterspinous stabilization devices, and further readily compensates forgraft settling so as to maintain continued axial loading of the graft. Amounting plate of the interspinous fusion device may be secured to abody portion therein in either a fixed or poly-axial manner so as toprovide better stability in lateral bending and rotation.

Some of the indications for use of the interspinous fusion device ofthis invention may include: (1) supplemental fixation for anteriorlumbar interbody fusion (ALIF) procedures; (2) supplemental fixation fortransforaminal lumbar interbody fusion TLIP) procedures; (3)supplemental fixation lateral interbody fusion procedures; (4) posteriorinterlaminar fusion; (5) posterolateral fusion; (6) fusion in parsdefect with facet pedicular screw; (7) fusion in Grade I spondolystheis;and (8) revision option in failed fusion/hybrid constructs.

Various aspects of this invention will become apparent to those skilledin the art from the following detailed description of the variousembodiments of the invention, when read in light of the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a first embodiment of an interspinousfusion device in accordance with this invention.

FIG. 2 is a front elevational view of the first embodiment of theinterspinous fusion device illustrated in FIG. 1.

FIG. 3 is a rear elevational view of the first embodiment of theinterspinous fusion device illustrated in FIGS. 1 and 2.

FIG. 4 is a side elevational view of the first embodiment of theinterspinous fusion device illustrated in FIGS. 1 through 3.

FIG. 5A is a side elevational view of a modified version of the firstembodiment of the interspinous fusion device illustrated in FIG. 4.

FIG. 5B is a schematic view of a movement-limiting mechanism that can beused with the modified version of the first embodiment of theinterspinous fusion device illustrated in FIG. 5A.

FIG. 6 is a perspective view of a portion of a second embodiment of aninterspinous fusion device in accordance with this invention.

FIG. 7 is an enlarged view of a portion of the second embodiment of theinterspinous fusion device illustrated in FIG. 6.

FIG. 8 is a front elevational view of the second embodiment of theinterspinous fusion device illustrated in FIGS. 6 and 7.

FIG. 9 is a side elevational view of the second embodiment of theinterspinous fusion device illustrated in FIGS. 6 through 8.

FIG. 10 is an enlarged front elevational view of a poly-axial mountingplate that can be used with the second embodiment of the interspinousfusion device illustrated in FIGS. 6 through 9.

FIG. 11 is a perspective view of the poly-axial mounting plateillustrated in FIG. 10.

FIG. 12 is a further enlarged front elevational view of a modifiedportion of the poly-axial mounting plate illustrated in FIGS. 10 and 11.

FIGS. 13 through 18 are perspective views of alternative embodiments ofthe poly-axial mounting plate illustrated in FIGS. 9 through 12.

FIG. 19 is a perspective view of a third embodiment of an interspinousfusion device in accordance with this invention.

FIG. 20 is a front elevational view of the third embodiment of theinterspinous fusion device illustrated in FIG. 19.

FIG. 21 is a side elevational view of the third embodiment of theinterspinous fusion device illustrated in FIGS. 19 and 20.

FIG. 22 is a perspective view of a fourth embodiment of an interspinousfusion device in accordance with this invention.

FIG. 23 is a side elevational view of the fourth embodiment of theinterspinous fusion device illustrated in FIG. 22.

FIG. 24 is a top plan view of the fourth embodiment of the interspinousfusion device illustrated in FIGS. 22 and 23.

FIGS. 25 and 26 are rear elevational views of modified versions of thepivotable mounting plates illustrated in FIGS. 22 through 24.

FIG. 27 is a perspective view of a fifth embodiment of an interspinousfusion device in accordance with this invention.

FIG. 28 is a side elevational view of the fifth embodiment of theinterspinous fusion device illustrated in FIG. 27.

FIG. 29 is a perspective view of a bone graft material that can be usedwith the fifth embodiment of the interspinous fusion device or any ofthe other embodiments of the interspinous fusion device describedherein.

FIG. 30 is a side elevational view of the bone graft materialillustrated in FIG. 29.

FIG. 31 is a perspective view of a modified version of the fifthembodiment of the interspinous fusion device illustrated in FIGS. 27 and28.

FIG. 32 is a front end elevational view of the modified version of thefifth embodiment of the interspinous fusion device illustrated in FIG.31.

FIG. 33 is a perspective view of a sixth embodiment of an interspinousfusion device in accordance with this invention.

FIG. 34 is a side elevational view of the sixth embodiment of theinterspinous fusion device illustrated in FIG. 33.

FIG. 35 is a rear end elevational view of the sixth embodiment of theinterspinous fusion device illustrated in FIGS. 33 and 34.

FIG. 36 is an exploded perspective view of a seventh embodiment of aninterspinous fusion device in accordance with this invention.

FIG. 37 is a perspective view of a first portion of the seventhembodiment of an interspinous fusion device illustrated in FIG. 36.

FIG. 38 is a perspective view of a second portion of the seventhembodiment of an interspinous fusion device illustrated in FIGS. 36 and37.

DESCRIPTION OF THE EMBODIMENTS

Referring now to the drawings, there is illustrated in FIGS. 1 through 4a first embodiment of an interspinous fusion device, indicated generallyat 10, in accordance with this invention. The interspinous fusion device10 includes a central body portion that is defined by a bottom wall 11,first and second opposed side walls 12 and 13, and a rear wall 14. Thebottom wall 11, the side walls 12 and 13, and the rear wall 14 cooperateto define a partially enclosed space, the purpose of which will beexplained below. The side walls 12 and 13 have respective inwardlyfacing serrated surfaces 12 a and 13 a provided thereon. Also, the sidewalls 12 and 13 have respective apertures 12 b and 13 b formedtherethrough. The purposes for these structures will also be explainedbelow.

As best shown in FIG. 4, a slot 14 a is formed between portions of theside walls 12 and 13 and the rear wall 14 so as to define a spring-likehinge between the bottom wall 11 and the rear wall 14 of theinterspinous fusion device 10. This spring-like hinge allows a limitedamount of pivoting movement of the rear wall 14 relative to the bottomwall 11. The purpose for allowing this pivoting movement will beexplained below.

First and second mounting plates 16 and 17 are respectively secured tothe rear wall 14 of the interspinous fusion device 10, extendingupwardly therefrom above the side walls 12 and 13, respectively. Themounting plates 16 and 17 have respective inwardly facing serratedsurfaces 16 a and 17 a provided thereon, the purpose of which will beexplained below. First and second mounting plates 18 and 19 arerespectively secured to the upper ends of the first and second mountingplates 16 and 17. In the illustrated embodiment, the mounting plates 18and 19 extend laterally outwardly in opposite directions from the upperends of the mounting plates 16 and 17, although such is not required.Each of the illustrated mounting plates 18 and 19 is shaped having atorsional twist as it extends laterally outwardly from the associatedbrackets 16 and 17. However, the mounting plates 18 and 19 may have anydesired shape or combination of shapes. Additionally, the mountingplates 18 and 19 need not be fixed in position relative to theassociated brackets 16 and 17, but rather may be movable relativethereto in a poly-axial manner, as described below. In either event, themounting plates 18 and 19 have respective apertures 18 a and 19 a formedtherethrough for a purpose that will be explained below.

First and second connecting plates 20 and 21 are respectively secured tothe lower ends of the first and second side walls 12 and 13 of thecentral body portion of the interspinous fusion device 10. In theillustrated embodiment, the connecting plates 20 and 21 are eachgenerally planar and extend parallel to one another. However, theconnecting plates 20 and 21 may have any desired shape or combination ofshapes. The connecting plates 20 and 21 have respective slot-shapedapertures 20 a and 21 a formed therethrough. The purposes for theconnecting plates 20 and 21 and the slot-shaped apertures 20 a and 21 awill be explained below.

The interspinous fusion device 10 is adapted to be secured to pair ofadjacent vertebrae (not shown) in a spine to stabilize the relativepositioning therebetween and to facilitate the placement of abone-growth material, such as a bone graft material, to enhance bonegrowth and fusion of the adjacent vertebrae. To accomplish this, thefirst and second mounting plates 18 and 19 are adapted to be secured toan upper one of the pair of adjacent vertebrae. To accomplish this, theinterspinous fusion device 10 is initially positioned such that thefirst and second mounting plates 18 and 19 are disposed adjacent torespective facets or other portions of the upper vertebra. Then, one ormore fasteners (not shown), such as conventional bone screws, can beinserted through each of the apertures 18 a and 19 a into engagementwith the adjacent facets or other portions of the upper vertebra. Inthis manner, the first and second mounting plates 18 and 19 of theinterspinous fusion device 10 can be secured to the upper one of thepair of adjacent vertebrae.

As shown in the drawings, either or both of the apertures 18 a and 19 aformed through the first and second mounting plates 18 and 19 can beshaped to permit the fasteners to extend therethrough at multiplelocations. In the illustrated embodiment, both of the apertures 18 a and19 a are irregularly shaped so as to define plural discrete positions onthe mounting plates 18 and 19 through which the fasteners may extendinto engagement with the adjacent facets or other portions of the uppervertebra. These plural discrete positions provide desirable flexibilityduring the installation process, inasmuch as the geometries of each ofthe upper pair of adjacent vertebrae can vary in accordance with thespecific anatomy of the patient. The interspinous fusion device 10 ofthis invention can readily accommodate such variations in anatomybecause the fasteners can be provided at any selected one of the pluraldiscrete positions defined by the apertures 18 a and 19 a that is deemedto be most appropriate based upon such anatomy.

Additionally, as discussed above, the illustrated mounting plates 18 and19 extend laterally outwardly in opposite directions from the upper endsof the side walls 12 and 13, and each is shaped having a torsionaltwist. The shapes of the first and second mounting plates 18 and 19 aresuch that relatively large surface areas thereof engage the respectivefacets or other portions of the upper vertebra. Such relatively largesurface area engagement functions to distribute load forces imparted bythe interspinous fusion device 10 more evenly across the surface areasof the respective facets or other portions of the upper vertebra. As aresult, the generation of undesirable localized stresses on the facetsor other portions of the upper vertebra is substantially reduced oravoided.

The first and second connecting plates 20 and 21 of the interspinousfusion device are adapted to be secured to a lower one of the pair ofadjacent vertebrae. To accomplish this, the interspinous fusion device10 is initially positioned such that the first and second connectingplates 20 and 21 are disposed about a spinous process or other portionof the lower vertebra. Then, one or more fasteners (not shown), such asconventional bone screws, can be inserted through each of theslot-shaped apertures 20 a and 21 a of the connecting plates 20 and 21and through the spinous process or other portion of the lower vertebra.In this manner, the first and second connecting plates 20 and 21 of theinterspinous fusion device 10 can be secured to the lower one of thepair of adjacent vertebrae.

As mentioned above, the bottom wall 11, the side walls 12 and 13, andthe rear wall 14 cooperate to define a partially enclosed space withinthe interspinous fusion device 10. This partially enclosed space can beused to receive a quantity of a bone-growth material, such as a bonegraft material, to enhance bone growth and fusion of the adjacentvertebrae. The partially enclosed space within the interspinous fusiondevice further functions to prevent the bone-growth material fromundesirably flowing out of the region between the adjacent vertebrae.The inwardly facing serrated surfaces 12 a and 13 a and the apertures 12b and 13 b on the side walls 12 and 13 provide irregularly shapedsurfaces that are well adapted to be engaged by the bone-growthmaterial, thereby functioning to positively retain such material withinthe central body portion of the interspinous fusion device 10. Themounting inwardly facing serrated surfaces 16 a and 17 a of the mountingplates 16 and 17 function in the same manner.

As also mentioned above, the interspinous stabilization device 10 ofthis invention not only more evenly distributes loads throughout theadjacent vertebrae than known interspinous stabilization devices, butalso can readily compensate for graft settling so as to maintaincontinued axial loading of the graft material disposed between theadjacent vertebrae. In the interspinous stabilization device 10 of thisinvention, this is accomplished by the provision of the two slot-shapedapertures 20 a and 21 a formed through the connecting plates 20 and 21.During the above-described installation process, the first and secondconnecting plates 20 and 21 are disposed about a spinous process orother portion of the lower vertebra, and a fastener is inserted throughthe slot-shaped apertures 20 a and 21 a and through the spinous processof the lower vertebra. As settling of the bone graft material occurs,the fastener can slide through the slot-shaped apertures 20 a and 21 a,thereby allowing the distance between the two adjacent vertebrae todecrease as settling of the bone graft occurs. Consequently, the axialpressure exerted by such adjacent vertebrae on the bone graft materialis effectively maintained as settling of the bone graft material occurs.

Additionally, as also described above, the slot 14 a formed betweenportions of the side walls 12 and 13 and the rear wall 14 defines aspring-like hinge between the bottom wall 11 and the rear wall 14 of theinterspinous fusion device 10. This spring-like hinge allows a limitedamount of pivoting movement of the rear wall 14 relative to the bottomwall 11. As a result, the axial pressure exerted by such adjacentvertebrae on the bone graft material is effectively maintained assettling of the bone graft material occurs.

Thus, the dynamic system of this invention is designed to take fulladvantage of Wolff s law of dynamic osteosynthesis. By avoiding stressshielding and allowing full load sharing, earlier and more substantialgraft incorporation can occur. The unique slot-shaped apertures 20 a and21 a and slot 14 a are designed to compensate for graft setting (bonegraft or special scaffold material, such as calcium phosphate, etc.) soas to maintain continued axial loading on the graft. Axial settling,which allows full load sharing capability, occurs because the fastenersare free to move through the slot-shaped apertures 20 a and 21 formedthrough the first and second connecting plates 20 and 21 and because thespring-like hinge defined between the bottom wall 11 and the rear wall14 of the interspinous fusion device 10 allows a limited amount ofpivoting movement of the mounting plates 16 and 17 (which are connectedto the upper vertebra) relative to the connecting plates 20 and 21(which are connected to the lower vertebra). As a result, the amount ofthis settling distance is determined by the amount of graft resorption,not because of any physical restriction imposed by the interspinousstabilization device 10 of this invention. Also, compression of the bonegraft material as explained above is facilitated.

Referring now to FIGS. 5A and 5B, there is illustrated a modifiedversion 10′ of the first embodiment of the interspinous fusion deviceillustrated in FIGS. 1 through 4, wherein like reference numbers areused to identify similar structures. In this modified version 10′, amovement-limiting mechanism, indicated generally at 15, is provided with(or in lieu of) the spring-like hinge to limit the pivoting movement ofthe mounting plates 16 and 17 relative to the connecting plates 20 and21 to a single rotational direction. An exemplary structure of themovement-limiting mechanism 15 is illustrated in FIG. 5B. As showntherein, the movement-limiting mechanism 15 can include an outer ring 15a that is secured to one of the bottom wall 11 and the rear wall 14, aninner hub 15 b that is secured to the other of the bottom wall 11 andthe rear wall 14, and one or more spring-loaded balls 15 c disposedbetween the outer ring 15 a and the inner hub 15 b. The spring-loadedballs 15 c cooperate with the outer ring 15 a and the inner hub 15 b ina manner that is well known in the art to allow relative movement tooccur only in one rotation direction. As a result, the movement-limitingmechanism 15 may be used to restrict the pivoting movement of the rearwall 14 relative to the bottom wall 11 to allow extension of the jointbetween the adjacent vertebrae but not flexion. It will be appreciatedthat the movement-limiting mechanism 15 may also be used in connectionwith any of the embodiments described herein.

Referring now to FIGS. 6 through 11, there is illustrated a secondembodiment of an interspinous fusion device, indicated generally at 110,in accordance with this invention. The second embodiment of theinterspinous fusion device 110 is similar to the first embodiment of theinterspinous fusion device 10 described above, and like referencenumbers (incremented by 100) are used to indicate similar structures. Inthis second embodiment of the interspinous fusion device 110, however,the mounting plates 118 and 119 (see FIGS. 10 and 11) are not fixed inposition relative to the upper ends of the first and second mountingplates 116 and 117. Rather, the mounting plates 118 and 119 arerespectively secured to the upper ends of the first and second mountingplates 116 and 117 in a manner that allows for poly-axial or otherrelative movement.

In the illustrated embodiment, this is accomplished by providing each ofmounting plates 116 and 117 with a mounting structure 116 b and 117 b,and further by providing each of the mounting plates 118 and 119 with acooperating mounting structure 118 a and 119 a. As shown in FIGS. 6through 9, the illustrated mounting structures 116 b and 117 b aregenerally hollow and cylindrical in shape and extend laterally outwardlyin opposite directions from the associated mounting plates 116 and 117.Each of the hollow cylindrical mounting structures 116 b and 117 b hasan outer surface, an inner surface, and a transverse aperture thatextends from the outer surface to the inner surface. As shown in FIGS.10 and 11, the illustrated mounting structures 118 a and 119 a of themounting plates 118 and 119 are generally spherical in shape. Thespherical mounting structures 118 a and 119 a of the mounting plates 118and 119 are sized and shaped to fit snugly within the hollow cylindricalmounting structures 116 b and 117 b of the mounting plates 116 and 117.As a result, the positions of the mounting plates 118 and 119 relativeto the associated mounting plates 116 and 117 can be adjusted in apoly-axial manner to correspond with the anatomy of the vertebra towhich they are secured, as described above. When a desired relativepositioning has been achieved, the mounting plates 118 and 119 can belocked in those relative positions by set screws (not shown) that extendrespectively through each of the transverse apertures formed through thehollow cylindrical mounting structures 116 b and 117 b of the mountingplates 116 and 117 into engagement with the spherical mountingstructures 118 a and 119 a of the mounting plates 118 and 119. However,the mounting plates 118 and 119 can be locked in those relativepositions by any desired means.

As shown in FIG. 6, the inner surfaces of the hollow cylindricalmounting structures 116 b and 117 b of the mounting plates 116 and 117are smooth. However, if desired, such inner surfaces of the hollowcylindrical mounting structures 116 b and 117 b may be formed having aserrated or other irregular shape, such as shown at 116 b′ in FIG. 7.Such irregular shape can provide an enhanced locking capability oversmooth inner surface. Similarly, as shown in FIGS. 10 and 11, the outersurfaces of the spherical mounting structures 118 a and 119 a of themounting plates 118 and 119 are smooth. However, if desired, such outersurfaces of the spherical mounting structures may be formed having aserrated or other irregular shape, such as shown at 118 a′ and 119 a′ inFIG. 12. Such irregular shape can similarly provide an enhanced lockingcapability over smooth outer surface. Either or both of the innersurfaces of the hollow cylindrical mounting structures 116 b and 117 band the outer surfaces of the spherical mounting structures 118 a and119 a may be formed in this manner.

FIGS. 13 through 18 are perspective views of alternative embodiments ofone of the poly-axial mounting plates 118 illustrated in FIGS. 9 through12.

In FIGS. 13 and 14, a first modified mounting plate 119-1 is curved fromend to end, has a generally uniform thickness throughout, and has agenerally uniform width throughout.

In FIG. 15, a second modified mounting plate 119-2 is linear from end toend, has a thickness that varies from a relatively thick portionadjacent to the mounting structure to a relatively thin portion adjacentan outer end thereof, and has a width that varies from a relativelynarrow portion adjacent to the mounting structure to a relatively wideportion adjacent the outer end thereof. In FIG. 16, a third modifiedmounting plate 119-3 has a torsional twist from end to end, has agenerally uniform thickness throughout, and has a width that varies froma relatively narrow portion adjacent to the mounting structure to arelatively wide portion adjacent an outer end thereof. In FIG. 17, afourth modified mounting plate 119-4 is linear from end to end, has athickness that varies from a relatively thin portion adjacent to themounting structure to a relatively thick portion adjacent an outer endthereof, and has a width that is generally uniform throughout. Lastly,in FIG. 18, a fifth modified mounting plate 119-5 is shaped having atorsional twist from end to end, has a generally uniform thicknessthroughout, and has a generally uniform width throughout.

Referring now to FIGS. 19 through 21, there is illustrated a thirdembodiment of an interspinous fusion device, indicated generally at 210,in accordance with this invention. The third embodiment of theinterspinous fusion device 210 is similar to the first embodiment of theinterspinous fusion device 10 described above, and like referencenumbers (incremented by 200) are used to indicate similar structures. Inthis third embodiment of the interspinous fusion device 210, however,the mounting plates 216 and 217 have respective slot-shaped apertures216 a and 217 a formed therethrough, and the mounting plates 18 and 19are eliminated. In this embodiment, rather, the mounting plates 216 and217 are secured directly to respective portions of the upper vertebra ina manner that is similar to how the connecting plates 20 and 21 aresecured directly to respective portions of the lower vertebra, asdescribed above. The slot-shaped apertures 216 a and 217 a function in amanner that is similar to the slot-shaped apertures 20 a and 21 a tomaintain the axial pressure exerted by the adjacent vertebrae on thebone graft as settling of the bone graft material occurs.

Referring now to FIGS. 22 through 24, there is illustrated a fourthembodiment of an interspinous fusion device, indicated generally at 310,in accordance with this invention. The fourth embodiment of theinterspinous fusion device 310 is similar to the first embodiment of theinterspinous fusion device 10 described above, and like referencenumbers (incremented by 300) are used to indicate similar structures. Inthis fourth embodiment of the interspinous fusion device 310, however,the side walls 312 and 313 are connected to the back wall 314 byrespective first hinges 315 a. Thus, the side walls 312 and 313 can bepivoted inwardly and outwardly relative to one another and relative tothe back wall 314 as desired. Similarly, the mounting plates 316 and 317are connected to the back wall 314 by respective second hinges 315 b.Thus, the mounting plates 316 and 317 can be pivoted inwardly andoutwardly relative to one another and relative to the back wall 314 asdesired. Consequently, the interspinous fusion device 310 can readilyaccommodate variations in the anatomy of the vertebrae to which theinterspinous fusion device 310 is attached, as described above.

FIGS. 25 and 26 are rear elevational views of alternative embodiments ofthe pivotable mounting plates 318′ and 319′ illustrated in FIGS. 22through 24. In addition to the apertures 318 a′ and 319 a′ formedrespectively therethrough, each of the mounting plates 318′ and 319′ hasone or more protrusions 318 b′ and 319 b′ formed thereon. Theprotrusions 318 b′ and 319 b′ are adapted to engage respective portionsof the associated vertebra to provide a more positive locking engagementtherewith and to more evenly distributes loads throughout.

Referring now to FIGS. 27 and 28, there is illustrated a fifthembodiment of an interspinous fusion device, indicated generally at 410,in accordance with this invention. The fifth embodiment of theinterspinous fusion device 410 includes a central body portion that isdefined by first and second opposed lower side walls 411 and 412, a rearwall 413, and first and second opposed upper side walls 414 and 415. Thefirst and second opposed lower side walls 411 and 412 have respectiveupper surfaces 411 a and 412 a provided thereon, while the first andsecond opposed upper side walls 414 and 415 have respective lowersurfaces 414 a and 415 a provided thereon. If desired, some or all ofthe surfaces 411 a, 412 a, 414 a, and 415 a may be defined byembossments or other raised structures provided as shown in FIGS. 27 and28, although such is not required. The first and second opposed lowerside walls 411 and 412, the rear wall 413, and the first and secondopposed upper side walls 414 and 415 cooperate to define a partiallyenclosed space, the purpose of which will be explained below.

As best shown in FIG. 28, the rear wall 413 defines a spring-like hingebetween the lower side walls 411 and 412 and the upper side walls 414and 415. A slit 415 c (see FIG. 28) or other gap or space is definedbetween the upper surfaces 411 a and 412 a of the lower side walls 411and 412 and the lower surfaces 414 a and 415 a of the upper side walls414 and 415. The slit 415 c may have any desired shape or size. However,it has been found desirable that the slit 415 c have a front-to-rearlength L (see FIG. 28) of about 12 mm. As also best shown in FIG. 28, itis desirable that the top-to-bottom height of the slit 415 c increasesfrom the rear to the front thereof. The angular relationship between theupper surfaces 411 a and 412 a of the lower side walls 411 and 412 andthe lower surfaces 414 a and 415 a of the upper side walls 414 and 415can vary as desired. However, an angular relationship of about 2° hasbeen found to be desirable.

First and second mounting plates 416 and 417 are respectively secured tothe upper side walls 414 and 415. The mounting plates 416 and 417 haverespective apertures 416 a and 417 a or other structures providedthereon to facilitate the securement of the interspinous fusion device410 to an upper one of the pair of adjacent vertebrae, as describedabove. In the illustrated embodiment, the mounting plates 416 and 417are each generally planar and extend parallel to one another. However,the mounting plates 416 and 417 may have any desired shape orcombination of shapes. Similarly, first and second connecting plates 420and 421 are respectively secured to the lower side walls 414 and 415.The connecting plates 420 and 421 have respective apertures 420 a and421 a or other structures provided thereon to facilitate the securementof the interspinous fusion device 410 to a lower one of the pair ofadjacent vertebrae, as also described above. In the illustratedembodiment, the connecting plates 420 and 421 are each generally planarand extend parallel to one another. However, the connecting plates 420and 421 may have any desired shape or combination of shapes.

FIGS. 29 and 30 illustrate a quantity of a bone graft material,indicated generally at 450, that can be used with the fifth embodimentof the interspinous fusion device 410 or any of the other embodiments ofthe interspinous fusion device described herein. The illustrated bonegraft material 450 is generally rectilinear in shape (although such isnot required) and includes an upper surface 451, a lower surface 452, afront end 453, and a rear end 454. The bone graft material 450 isadapted to be disposed within the interspinous fusion device 410 withthe upper surface 451 adjacent to the lower surfaces 414 a and 415 a ofthe upper side walls 414 and 415, the lower surface 452 adjacent to theupper surfaces 411 a and 412 a of the lower side walls 411 and 412, andthe rear end 454 adjacent to the rear wall 413. The angular relationshipbetween the upper and lower surfaces 451 and 452 of the bone graftmaterial 450 can vary as desired. However, as best shown in FIG. 30, thetop-to-bottom distance between the upper and lower surfaces 451 and 452of the bone graft material 450 preferably gets larger from the front end453 to the rear end 454. The top-to-bottom distance between the upperand lower surfaces 451 and 452 of the bone graft material 450 can, forexample, vary in the range of from about 1° to about 5°, preferablyabout 2°.

The relationship between the size and shape of the gap 415 c in theinterspinous fusion device 410 and the size and shape of the bone graftmaterial 450 is advantageous. In particular, it is desirable that thisrelationship be such that a relatively high compression be placed uponthe bone graft material 450 while imposing a relatively low stress onthe interspinous fusion device 410. The relatively high compressionplaced upon the bone graft material 450 facilitates that the bone graftmaterial 450 remain in a desired position relative to the interspinousfusion device 410 and, thus, to the vertebrae to which the interspinousfusion device 410 is to be secured. The relatively low stress imposedupon the interspinous fusion device 410 minimizes the likelihood thatdamage may occur during or after installation of the bone graft material450. The interspinous fusion device 410 may be formed from any desiredmaterial including, but not limited to, polyether ether ketone (PEEK),titanium, nitinol (nickel titanium), cortical bone, and composites.

FIGS. 31 and 32 illustrate a variation 410′ on the fifth embodiment ofthe interspinous fusion device 410 illustrated in FIGS. 27 and 28, andlike reference numbers are used to indicate similar structures. In thisvariation, the interspinous fusion device 410′ includes first and secondmounting plates 418′ and 419′ that are respectively secured to the upperends of the first and second mounting plates 416′ and 417′. Like thevarious mounting plates discussed above, the first and second mountingplates 418′ and 419′ may have any desired shape or combination ofshapes, may be fixed in position relative to the respective mountingplates 416′ and 417′ (as illustrated) or movable relative thereto (suchas shown in FIGS. 6 through 18), and may include one or more apertures(not shown) to facilitate the securement of the interspinous fusiondevice 410′ to respective ones of the upper pair of adjacent vertebrae,all as described above.

Referring now to FIGS. 33 through 35, there is illustrated a sixthembodiment of an interspinous fusion device, indicated generally at 510,in accordance with this invention. The sixth embodiment of theinterspinous fusion device 510 is similar to the fourth embodiment ofthe interspinous fusion device 410 described above, and like referencenumbers (incremented by 100) are used to indicate similar structures. Inthis sixth embodiment of the interspinous fusion device 510, however,the rear wall of the interspinous fusion device 510 is defined by ahinge, indicated generally at 513, that includes a first portion 513 athat is formed integrally with or connected to the lower side walls 511and 512 and a second portion 513 b that is formed integrally with orconnected to the lower side walls 511 and 512. A pivot pin 513 c extendsthrough aligned apertures (not shown) formed through the first andsecond portions 513 a and 513 b such that the lower side walls 511 and512 can pivot relative to the upper side walls 514 and 515 in a jaw-likemanner. A locking nut 513 d may be threaded onto the end of (orotherwise secured to) the pivot pin 513 c. The locking nut 513 d can beselectively operated (typically tightened on the pivot pin 513 c) so asto retain the lower side walls 511 and 512 in a desired positionrelative to the upper side walls 514 and 515.

In use, the sixth embodiment of the interspinous fusion device 510 isinstalled by initially releasing the locking nut 513 d so that the lowerside walls 511 and 512 are free to pivot relative to the upper sidewalls 514 and 515. Then the interspinous fusion device 510 is installedby securing the mounting plates 416 and 417 to an upper one of the pairof adjacent vertebrae, and further by securing the connecting plates 420and 421 to a lower one of the pair of adjacent vertebrae, as alsodescribed above. Thereafter, the locking nut 513 d is tightened on thepivot pin 513 c so as to maintain the lower side walls 511 and 512 in apredetermined position relative to the upper side walls 514 and 515.This structure allows the spacing between the first and second opposedlower side walls 511 and 512 and the first and second opposed upper sidewalls 514 and 515 to be customized to the specific anatomy of thepatient.

Referring now to FIGS. 36 through 38, there is illustrated a seventhembodiment of an interspinous fusion device, indicated generally at 610,in accordance with this invention. The seventh embodiment of theinterspinous fusion device 610 is similar to the fourth embodiment ofthe interspinous fusion device 410 described above, and like referencenumbers (incremented by 200) are used to indicate similar structures. Inthis seventh embodiment, however, the interspinous fusion device 610 issplit into two separate lateral portions 610 a and 610 b that aresupported on one another. To accomplish this, the first portion 610 ahas a protrusion 613 b provided thereon that extends laterally towardthe second portion 6106 of the interspinous fusion device 610.Similarly, the second portion 610 a has a recess 613 a provided thereonthat faces laterally toward the first portion 610 a of the interspinousfusion device 610. Preferably, the recess 613 a and the protrusion 6136are sized and shaped in a complementary manner, such as the illustratedU-shaped configurations. However, the recess 613 a and the protrusion613 b may be formed having any desired sizes and shapes, as well ascombinations thereof.

The interspinous fusion device 610 is assembled by initially aligningthe protrusion 613 b provided on the first portion 610 a with the recess613 a provided on the second portion 610 b as shown in FIG. 36. Then,the first and second portions 610 a and 610 b are moved toward oneanother such that the protrusion 613 b is received within the recess 613a. Preferably, the recess 613 a and the protrusion 613 b are sized andshaped so that relative lateral movement is permitted withoutsignificant other looseness therebetween. This structure allows thelateral spacing between the mounting plates 616 and 617 and/or betweenthe connecting plates 620 and 621 to be customized to the specificanatomy of the patient. If desired, a locking mechanism (not shown) canbe provided to maintain the first and second portions 610 a and 610 b ina desired lateral orientation relative to one another.

The principle and mode of operation of this invention have beenexplained and illustrated in its various embodiments. However, it mustbe understood that this invention may be practiced otherwise than asspecifically explained and illustrated without departing from its spiritor scope.

What is claimed is:
 1. An interspinous stabilization device comprising:a body portion; a pair of mounting plates supported on the body portionand adapted to engage a first vertebra; and a pair of connecting platessupported on the body portion and adapted to engage a second vertebra,wherein the interspinous stabilization device is adapted to maintaincontinued axial loading of a graft disposed between the first and secondvertebra as settling of the graft occurs.
 2. The interspinousstabilization device defined in claim 1, wherein one or both of themounting plates are shaped having a torsional twist.
 3. The interspinousstabilization device defined in claim 1, wherein one or both of themounting plates has an aperture formed therethrough that is shaped topermit a fastener to extend therethrough at multiple locations.
 4. Theinterspinous stabilization device defined in claim 1, wherein one orboth of the connecting plates has a slot-shaped aperture formedtherethrough.
 5. The interspinous stabilization device defined in claim1, wherein the body portion is defined by a bottom wall, first andsecond opposed side walls, and a rear wall that cooperate to define apartially enclosed space for the receipt of a bone graft material. 6.The interspinous stabilization device defined in claim 1, wherein one orboth of the mounting plates is fixed in position relative to the bodyportion.
 7. The interspinous stabilization device defined in claim 1,wherein one or both of the mounting plates is movable relative to thebody portion and lockable in a desired position relative thereto.
 8. Theinterspinous stabilization device defined in claim 1, wherein the bodyportion is defined by a bottom wall, first and second opposed sidewalls, and a rear wall, and wherein a hinge is provided between thebottom wall and the rear wall to allow relative pivoting movementtherebetween.
 9. The interspinous stabilization device defined in claim8, further including a movement-limiting mechanism to restrict thepivoting movement of the rear wall relative to the bottom wall to asingle rotational direction.
 10. The interspinous stabilization devicedefined in claim 1, wherein one or both of the mounting plates has agenerally uniform thickness.
 11. The interspinous stabilization devicedefined in claim 1, wherein one or both of the mounting plates varies inthickness from end to end.
 12. The interspinous stabilization devicedefined in claim 1, wherein one or both of the mounting plates is linearfrom end to end.
 13. The interspinous stabilization device defined inclaim 1, wherein one or both of the mounting plates is curved from endto end.
 14. The interspinous stabilization device defined in claim 1,wherein one or both of the mounting plates has a slot-shaped apertureformed therethrough.
 15. The interspinous stabilization device definedin claim 5, wherein one or both of the side walls are pivotablyconnected to the rear wall.
 16. The interspinous stabilization devicedefined in claim 5 wherein one or both of the mounting plates arepivotably connected to the rear wall.
 17. The interspinous stabilizationdevice defined in claim 1, wherein either or both of the pair ofmounting plates is pivotably supported on the body portion.
 18. Theinterspinous stabilization device defined in claim 1, wherein either orboth of the pair of connecting plates is pivotably supported on the bodyportion.
 19. The interspinous stabilization device defined in claim 1,wherein the body portion includes a spring-like hinge between the pairof mounting plates and the pair of connecting plates.
 20. Theinterspinous stabilization device defined in claim 19, wherein thespring-like hinge is defined by a slot that extends between the pair ofmounting plates and the pair of connecting plates.
 21. The interspinousstabilization device defined in claim 19, wherein the slot has a lengthof about 12 mm.
 22. The interspinous stabilization device defined inclaim 19, wherein the slot expands at an angular relationship of about2°.
 23. The interspinous stabilization device defined in claim 1,wherein the body portion includes a hinge between the pair of mountingplates and the pair of connecting plates.
 24. The interspinousstabilization device defined in claim 23, wherein the hinge includes apivot pin that extends through portions of the pair of mounting platesand the pair of connecting plates.
 25. The interspinous stabilizationdevice defined in claim 24, further including a mechanism formaintaining the pair of mounting plates in a predetermined positionrelative to the pair of connecting plates.
 26. The interspinousstabilization device defined in claim 25, wherein the mechanism formaintaining includes a locking nut provided on the pivot pin.
 27. Theinterspinous stabilization device defined in claim 1, wherein theinterspinous fusion device is split into two separate lateral portionsthat are supported on one another.
 28. The interspinous stabilizationdevice defined in claim 27, wherein a first lateral portion has aprotrusion provided thereon, and wherein a second lateral portion has arecess provided therein that receives the protrusion.
 29. Theinterspinous stabilization device defined in claim 28, wherein therecess and the protrusion are sized and shaped in a complementarymanner.
 30. The interspinous stabilization device defined in claim 28,wherein the recess and the protrusion are U-shaped.
 31. An interspinousstabilization device that is connected to a plate so as to directlystabilize a spinous process with a facet joint in a vertebra in a spine.